Project Summary Patients with pulmonary arterial hypertension (PAH) have impaired exercise capacity and reduced quality of life. Current therapies only modestly improve exercise capacity and are often prohibitively expensive, highlighting the need for additional, cost-effective interventions. Multiple studies have demonstrated that increasing physical activity is highly efficacious in PAH, resulting in six-minute walk distance (6MWD) improvement that exceeds the effect of medications. However, previously tested protocols have required inpatient rehabilitation, making them impractical and poorly scalable to the general PAH population. Moreover, cardiopulmonary rehabilitation is not reimbursed by insurance companies or Medicare in the United States underscoring the need for alternatives to promote physical activity. In preliminary work, we have shown that daily step counts are markedly reduced in PAH and associated with increased adverse events. We have also developed a fully-automated mobile health (mHealth) intervention that increased step counts in an ambulatory cardiology population in a randomized trial. The key feature of the intervention was the addition of a ?smart text? component delivered to the subject?s smartphone, which generated personalized, encouraging content based in behavioral change theory (e.g. feedback loops and habit formation). This aspect of the mHealth intervention alone increased step counts over 300% compared with blinded step count tracking. The proposed study will be the first to test the feasibility of an mHealth intervention in the PAH population. We hypothesize that an mHealth intervention is feasible and will increase step counts in subjects with PAH. We propose a randomized trial of unblinded step tracking with smart texts versus blinded tracking for 12 weeks. Participants will wear a display-free triaxial accelerometer, which will continuously transmit data to a compatible smartphone. We selected efficacy endpoints to mirror FDA criteria for drug approval in PAH. Aim 1 will test the feasibility of this intervention to increase step counts. We will also assess aerobic time and the fidelity of text and data transmission. In Aim 2, we will test the effect of this intervention on 6MWD and quality of life. Aim 3 will focus on potential mechanisms of improved exercise capacity with increased activity. We will assess right ventricular function and insulin/glucose homeostasis. This study will be the initial test of an mHealth intervention in the PAH population, designed to mirror trials of currently approved PAH therapies. The goals of this proposal are to 1) assess the feasibility of an mHealth intervention in the PAH population and 2) identify aspects of the protocol that may need to be refined for a larger trial in this population. In the last year of this award, we anticipate proposing a large, multi-center R01-funded Phase III trial of this intervention with our close collaborators across the country.